This invention relates to a hydraulic twin-pipe shock absorber for horizontal use, in particular for rail vehicles provided with a cylindrical housing, a fluid-filled working cylinder provided inside the housing, and a radial clearance between the housing and working cylinder. A piston is displaceable in the working cylinder and has a first connection which is located between the clearances on either side of the piston and can be shut-off by a first non-return value. A piston rod projects through a cover of the working cylinder. A second connection extends through the cover between the working cylinder and the radial clearance and can be shut-off by a second shut-off valve. A third connection is located between the radial clearance and the working cylinder clearance not containing the piston rod and can be shut-off by a third shut-off valve. The first non-return valve admits hydraulic fluid to the working cylinder part with the piston rod, the second non-return valve admits hydraulic fluid to the radial clearance, and the third non-return valve admits hydraulic fluid to the working cylinder part without the piston rod.
The hydraulic fluid can flow in only one direction through the working cylinder, namely from the working cylinder clearance without the cylinder rod passage to the working cylinder clearance with the cylinder rod passage, and from the latter clearance to the radial clearance. Such a circulating design means that the resistance during movement of the piston rod in two opposing directions can be essentially equal, which with the use of a horizontal absorber in a rail vehicle is of vital importance for satisfactory bend behavior.
The non-return valves are loaded in the closing direction by a spring, this means that before a valve can be opened by the hydraulic fluid, pressure must be built up. If there is air in the working cylinder, the pressure build-up will be uneven, which means that the first and second non-return valves do not always open in the same conditions and the resistance effect can be uneven. Air and possibly foam could also delay the moment of opening of the non-return valves. The air and the foam collect in the horizontal cylinder at the top against the cover which allows through the piston rod and against the piston. Dead spaces filled with the air or the foam are produced as a result. The object of the invention is to solve the problem of upsetting the uniformity of the action at the first connection.